1. Field of the Invention
The present invention pertains generally to electrical power dividers and specifically to methods for connecting one or more ports to a number of other ports in such a way that the amplitude and phase excitations of the ports can be controlled within close limits over a wide range of frequencies.
The invention more specifically pertains to Beam-forming Networks including power dividers having wide band frequency responses.
2. Description of Prior Art
Beam-forming Networks, or BFN's, are employed in many antenna applications to generate multiple beams or combinations of beams in both terrestrial and space-borne applications. In the former, BFN's can be used for the generation of spatially coincident beams at different frequencies. In the space-borne case, BFN's can be used to form shaped beams covering limited footprints on the earth's surface.
The BFN's are composed of a number of different parts, for example, radiating elements, interconnecting transmission lines, power dividing elements, phase shifters and transformers. The radiating elements are typically used for feeding a collimating objective, such as a lens or reflector, in such a way that an individual elemental beam is associated with each radiating element. The final beam configuration formed by the BFN in association with the objective is the vector sum of the elemental beams with amplitudes and phases determined by the design of the BFN. The BFN may also be used to feed an array of radiators forming several beams without the use of a collimating objective.
The principal part determining the amplitude excitations of the radiating elements is the power dividing part. In many systems, this part may take the form of a directional coupler of which several forms exist in many widely-used types of transmission lines. Typical directional couplers in which the power division ratio can be easily and conveniently altered include such devices as branch-line couplers, short slot hybrids, and proximity couplers.
One of the principal limitations in the design of BFN's is the relatively narrow bandwidth of the parts forming the BFN. Bandwidths up to 15% are typically required for many applications which require relatively stable variation of coupling radio and phase as a function of frequency. In the types of couplers described above, which, in their waveguide applications are suitable for very high radio-frequency powers, coupling ratio flatness of .+-.0.25 dB is achievable over these 15% bandwidths. At larger bandwidths, the flatness degrades.
In several instances, BFN's must be designed to accommodate widely separated frequency bands. For example, the BFN may have to carry a transmit band and a receive band of frequencies. Where the frequency separation is large, prior experience of the available bandwidth of power dividers has dictated that the individual BFN's be designed to separate the transmit and receive bands into two networks. The two networks are then combined by means of a number of frequency combining networks (or diplexers), one for each radiating element.
As will be appreciated, especially in space applications, it is desirable to reduce the weight of the space borne components as a reduction in weight means that less fuel is required to control the spacecraft. Accordingly, with the same fuel load, a lighter spacecraft will be able to stay aloft for a greater period of time.
It would therefore be desirable to provide a BFN whose frequency response is broad enough so that it is responsive to both receive and transmit frequencies. With such a BFN, only a single BFN would be needed for both the transmit and receive functions thus eliminating a complete BFN relative to the prior art. Such a BFN would not need a diplexer for each radiating element; the weight of such a BFN would be less than half of the weight of a presently existing BFN.